If you mean buying ghosts from Space Ben, I imagine he does run out, most you get from the ghost exchange, just wait around until the price is low and then buy a tonne.
Your supposed to sell when it's high, but usually Derek's Jerk busting got me more than enough Stardust.
Just stuck my head in to see if my savegame is still okay since I needed to mess with the itch.io cookies recently, and thankfully it is.
Still looking forward to chapter three and seeing what happens to poor burger.